What kind of star is Algenib?
Algenib, catalogued as Gamma Pegasi (γ Peg), appears in the official constellation Pegasus. Its apparent visual magnitude is about 2.82–2.86, while its estimated distance is about 470 light-years. Astronomers classify the object as B2 IV; hybrid pulsating variable. These labels describe temperature, luminosity class or system components; they should not be read as a claim that every naked-eye point is a single isolated star.
Gamma Pegasi is a hot B2 subgiant whose SIMBAD parallax corresponds to roughly 470 light-years, with the usual caution for a distant bright star. Precision photometry and spectroscopy reveal it as a hybrid pulsator: it shows both higher-frequency Beta Cephei-type pressure modes and lower-frequency slowly pulsating B-star gravity modes. Those oscillations travel through different parts of the stellar interior, constraining rotation, mixing and evolutionary state. Algenib is far more massive and luminous than the Sun and is beginning to evolve beyond core hydrogen burning. Its visual brightness seems nearly constant without instruments because the pulsation amplitudes are small. The other Great Square corners differ strongly in temperature, distance and age, proving that geometric asterisms do not imply shared formation.
The coordinate pair RA 00h 13m 14.15s, Dec +15° 11′ 01.0″ fixes the object's direction on the celestial sphere for the J2000 reference epoch. Right ascension works like celestial longitude measured in hours, while declination works like latitude north or south of the celestial equator. Proper motion and improved measurements can refine catalogue positions, but these coordinates are sufficiently precise for a finder chart or planetarium search.
Algenib data at a glance
| Proper name | Algenib | Catalogue designation | Gamma Pegasi (γ Peg) |
|---|---|---|---|
| Constellation | Pegasus | Apparent magnitude | about 2.82–2.86 |
| Spectral or system type | B2 IV; hybrid pulsating variable | Estimated distance | about 470 light-years |
| Right ascension (J2000) | 00h 13m 14.15s | Declination (J2000) | +15° 11′ 01.0″ |
Values are rounded for an observer-friendly overview. Consult the linked SIMBAD record for component-level identifiers, bibliography, measurement provenance and newer catalogue values.
The name Algenib
From Arabic al-janb, “the side” or “flank.” The same historical name was once also used for Alpha Persei, now standardized as Mirfak.
Algenib's “flank” description suits Pegasus's traditional body. Historical catalogues sometimes applied the same word to Alpha Persei, an ambiguity resolved by modern IAU standardization: Algenib now denotes Gamma Pegasi. Variable-star research later transformed this old navigational marker into a benchmark for hybrid B-star pulsation. The change illustrates why standardized proper names and stable catalogue designations both matter when historical labels have migrated between constellations.
Modern professional catalogues retain identifiers such as the Bayer designation alongside a proper name. The International Astronomical Union standardizes which name belongs to which component—an important distinction for systems whose combined light looks like one star from Earth.
How to find Algenib
Locate the Great Square and choose its southeastern corner, below Alpheratz. Algenib is easy without optical aid. Binocular sweeps eastward enter Pisces and Cetus, while its subtle pulsation requires precision instruments rather than visual watching.
Visible from most inhabited latitudes and best during northern autumn. Visibility on a particular night still depends on latitude, season, time, horizon obstructions, weather and local light pollution. Use the interactive atlas below to check the surrounding field before observing.
Observation checklist
- Best from September through November evenings.
- Use the Square's geometry for immediate identification.
- Do not expect to see its low-amplitude pulsations by eye.
- Compare its blue-white light with redder Scheat.
Interesting facts about Algenib
- Algenib is a hybrid Beta Cephei/SPB pulsator.
- It forms the Great Square's southeastern corner.
- The same name was historically used for Alpha Persei.
- It is an evolved early-B star.
- Its distance is approximately 470 light-years.
Continue from Algenib into the night sky
Use the Pegasus constellation guide to place this star within its larger pattern. When you are ready to observe, compare dark-sky places, find a nearby observatory, or follow our practical guide to finding a star in the night sky. Symbolically registered names are kept separately in the searchable Star-Register catalogue.
Sources and further reading
Measurements are rounded for readability. Multiple systems, variable stars and distant supergiants can have component-specific or model-dependent values. Survey panels show photographic sky fields, not the physical surface of the star.